1. Field of Invention
The present invention relates to a method and apparatus for inspecting a solderless terminal which has been crimped against one end portion of an electric conductor. More specifically, the invention relates to a method and apparatus for illuminating and image processing to inspect a solderless terminal to determine whether or not the solderless terminal has been satisfactorily crimped against an electric conductor.
2. Description of the Related Art
FIG. 21 shows a solderless terminal 2 comprising a cylindrical shaped resin barrel 2a holding a resin cover 1a near one end portion of an electric conductor 1 which has the resin cover 1a removed, a core wire barrel 2b which also has a cylindrical shape to hold the one end portion of the electric conductor 1 having the resin cover 1a removed, a plurality of core wires 1b comprising the electric conductor 1, and an end portion 2c which is engaged with a mating solderless terminal so as to be electrically connected to the solderless terminal. As shown in FIG. 21, bell mouths 10 are formed at both ends of the core wire barrel 2b to release stress produced by crimping the solderless terminal 2 against the electric conductor 1. Heretofore, an inspecting apparatus as shown in FIG. 22 has been used in inspecting the solderless terminal 2 by image processing.
To inspect how a solderless terminal and electric conductor are crimped, the solderless terminal must first be illuminated as described later. The image of a solderless terminal 2 produced by illumination is picked up by image pick-up means 3 such as a television camera or a two-dimensional CCD camera, and displayed on a monitoring television set or monitor. The image is processed by image processing means 5, so that the resulting luminance data of the picture elements of the image are utilized to determine the presence or absence of the resin cover 1a and the core wires 1b between the resin barrel 2a and the core wire barrel 2b. The resulting luminance data is also used to determine the exposure of the core wires 1b located between the core wire barrel 2b and the end portion 2c to judge whether or not the solderless terminal 2 has been satisfactorily crimped against an electric conductor. The results of these determinations are printed out by a printer 6, or displayed on a display unit 7. Further in FIG. 22, reference numeral 8 designates an operation keyboard, with which program data or the like are inputted for an image processing operation.
In the above-described method of inspecting a crimped solderless terminal, illumination of the solderless terminal plays an important role. A variety of methods for illuminating a solderless terminal are known. For instance, Japanese Patent Application (OPI) No. 60249 (the term "OPI" as used herein means an "unexamined published application") discloses an illuminating method in which contrast is obtained by using a resin cover formed of a certain complementary color. More specifically, a spot-like convergent light beam formed by an optical fiber is applied to the solderless terminal, and the light reflected therefrom is received by image pick-up means through a filter formed a color which is the complementary color of the resin color.
Japanese Patent Application (OPI) No. 175942 discloses a method in which contrast between a resin portion and a metal portion is obtained by using polarized light. Furthermore, Japanese Patent Application (OPI) No. 198473 discloses a method in which contrast between a resin portion and a metal portion is obtained by using a light beam of a particular wavelength which the resin material readily absorbs.
The above-described conventional illuminating methods have several drawbacks. Whenever a resin color is changed, it is necessary to select either a complementary color filter suitable for the new resin color, or a light beam having a wavelength suitable for the new resin color. That is, different complementary color filters or different light beams must be used for different resin colors thereby increasing the cost and required maintenance. In addition, it is impossible for either of the illuminating methods to accurately obtain the necessary contrast between a resin portion and metal portion. Thus, the conventional methods cannot accurately determine if a solderless terminal has been satisfactorily crimped against the electric conductor.